EVPN Type 4 (Ethernet Segment route) Explained

Ethernet Segment Routes are needed in multi-homing scenario and used for Designated Forwarder Election. Designated Forwarder is responsible for sending broadcast, unknown multicast and multicast (BUM) traffic to the CE on a particular Ethernet Segment.

RFC 7432 allows selecting a DF at the granularity of <ES, VLAN> for VLAN-based service and <ES, VLAN bundle> for VLAN-aware service. This enables load-balancing of BUM traffic at a VLAN or VLAN-bundle level.

Please refer to the following cheat sheet if you are not familiar with EVPN Terminology.

The format of Type 4 advertisement is as follows:

EVPN Type 3 Route Format

Let’s review Type 4 advertisements originated by PE5 in the following example: